In present day medical practice, hemodialysis is the standard therapy for treating ESRD. This therapy involves dialyzing the patient's blood several times a week. During treatment, the patient's vascular system is connected to a hemodialysis machine for sessions lasting several hours. This connection forms a blood circuit whereby blood is drawn from the patient through a needle connected to a patient access, cycled through a hemodialysis machine that removes waste products including water, urea, and other impurities from the blood, and returned to the patient access via a second blood line and needle.
The functional interface between the patient and the extracorporeal circuit is the patient or vascular access, from which blood is withdrawn and to which the externally treated blood is returned. To facilitate removal and return of blood, the patient access may have specialized connections allowing mating of separate arterial and venous blood lines, or the access may be cannulated with a hollow needle which is then connected to arterial and venous blood lines. Vascular access has been called the "Achilles' heel of dialysis" because of the frequent morbidity associated with maintenance and utilization of the access. A malfunctioning vascular access is not trivial, as the access represents a conduit for the passage of blood to the artificial kidney. Without treatment via the external kidney, toxin accumulation in the body is rapid and can be deadly.
One of the difficulties that can arise in chronic hemodialysis is maintaining adequate blood flow during treatment sessions. When flow rates decrease significantly during a session, the attendant could in many cases restore adequate flow by switching the blood lines. In current practice, the attendant must usually turn off the hemodialysis machine. This process lengthens the dialysis session while the machine is primed and restarted. In addition, switching the blood lines involves disconnecting the lines, which can cause bleeding and allow air to enter the lines. Disconnecting the lines also breaks the microbe barrier, increasing the possibility of infection.
Another difficulty that often arises with chronic hemodialysis is the possibility that the patient will develop a thrombus or blood clot that partially or wholly occludes a vascular access created by a fistula or vascular graft. When a fistula or graft becomes blocked, surgery is frequently needed to restore the venous access to a useful condition or replace the access site. A balloon angioplasty may be used to enlarge the lumen of the fistula or graft and prevent the immediate formation of thrombosis, thereby extending the life of the access. When a site can no longer be restored, it must be replaced. Replacing an access is a serious matter because patients have only a limited number of access sites for A/V fistulas and PTFE grafts.
Accordingly, an object of the present invention is to provide for the easy and convenient selection of which needle or catheter will be used to draw blood from the access and which will be used to return blood to the access at any particular time during hemodialysis treatment sessions, wherein such flow reversal can be employed in assessing access maintenance. Another object of this invention is to have a device that is compatible with high rates of flow in dialysis methods which utilize catheters. Yet another object of this invention is to accomplish the flow reversal function while minimizing the amount of turbulence associated with blood flow through the device. Still another object of the invention is to provide a device enhances safe use. A further object of the invention is to minimize stagnant flow regions in the device. Still another object of this invention is to provide a device that is easily added to existing hemodialysis set ups and treatment programs. Still another object of this invention is to provide a low cost, easily manufactured, sterile disposable device compatible with the rest of the blood circuit.